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American Community Survey. Susan Clapp Demographics & Workforce Group U.Va . Weldon Cooper Center for Public Service. What will I learn today?. ACS Basics ACS and the 2010 Census Accessing Data Using survey estimates What to watch out for Resources. What is the ACS?.

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American community survey

American Community Survey

Susan Clapp

Demographics & Workforce Group

U.Va. Weldon Cooper Center for Public Service

What will i learn today
What will I learn today?

  • ACS Basics

  • ACS and the 2010 Census

  • Accessing Data

  • Using survey estimates

  • What to watch out for

  • Resources

What is the acs
What is the ACS?

  • The American Community Survey (ACS) is an ongoing survey that provides data every year -- giving communities the current information they need to plan and to provide services.

  • Survey data help determine how more than $400 billion in federal and state funds are distributed each year.

American community survey 1353247

What is the ACS?




Where did the acs come from
Where did the ACS come from?

Continuous ACS replaced long form in 2005

  • The ACS has its roots in the Decennial Census long form.

Basics – age, gender, race, number of people

Details – income, education, language spoken, etc.

Short form Census every 10 years

Short form Census every 10 years

Short form and long form

Census every 10 years

How has the acs helped
How has the ACS helped?

  • Detailed data are available every year, not every 10 years

  • ACS interviewers are professional, year-round employees, not temporary employees hired every 10 years

  • Faster, cheaper, and more accurate Decennial Census

What about the 2010 census
What about the 2010 Census?

2010 Census



To show the


of people

To show



in the U.S. live

who live

in the U.S.


10 questions

69 questions


Once, April 1, 2010



How it should be used

To obtain

counts of the

To about the population’s

population and their basic

demographic, social, economic, and


housing characteristics

Who is questioned

The entire population

A sample of the population

(over 130

million households)

(approximately 3 million households

each year)

Type of data



with margins of error

What can we learn from the acs
What can we learn from the ACS?

Social Characteristics

Demographic Characteristics

Housing Characteristics

Economic Characteristics


Financial Characteristics

Who takes the survey
Who takes the survey?

  • Resident population of the United States and Puerto Rico – all people living in housing units and group quarters

    • A “group quarters” is a residence that is managed by an organization providing housing or services for residents (e.g. college dormitories, prisons, and nursing homes).


What do i need to know before i access the data
What do I need to know before I access the data?

  • Three different kinds of estimates (data series)

    • 5-year estimates for all geographic areas

    • 3-year estimates for areas with 20,000 or more

    • 1-year estimates for areas with 65,000 or more

  • Sample size (number of people surveyed) is not large enough to obtain annual estimates for small geographic areas

What are single and multi year estimates
What are single- and multi-year estimates?

  • Data series are named for length of time required to collect sufficient sample

    • e.g. 1-year estimates are based on data collected over a 1-year period

  • 3- and 5- year estimates are known as multi-year estimates because they are based on data collected over multiple years

Which estimates do i use
Which estimates do I use?

  • Use single-year estimates when…

    • Currency (timeliness) is critical

    • Researching large areas experience rapid change

    • Examining year-to-year changes

  • Use multi-year estimates when…

    • Reliability of the data is critical

    • Analyzing data for small areas

    • Studying smaller populations in large areas

    • Examining a set of areas in which some areas have only multi-year estimates

When are data released
When are data released?

  • New estimates are released every year for all three series

Year of Data Release

Data Series




Years of Data Collection































Access to data
Access to Data

  • American Factfinder


    • Albemarle County

    • Greene County

    • Albemarle and Greene

Census vs survey
Census vs. Survey




Margins of error
Margins of Error

  • Surveys have error. The ACS tables give you the margin of error so you can use the estimates appropriately.

What do i do with the margins of error
What do I do with the Margins of Error?

  • 1) Take a look at them

  • 2) Calculate the confidence interval

    • Confidence interval is a range – the Census Bureau is 90% confident that the true population statistic is between A and B

      A = Estimate – Margin of Error

      B = Estimate + Margin of Error

Calculating confidence intervals
Calculating Confidence Intervals

A = 490-139 = 351

B = 490+139 = 629

The Census Bureau is 90% confident that the true number of Greene county residents, ages 60 to 64 years old, who own their home, is between 351 and 629.

American community survey 1353247

Calculating Confidence Intervals

A = 50-57 = -7

B = 50+57 = 107

The Census Bureau is 90% confident that the true number of Greene county residents who are Asian, 16+, working, and commuting to work in their own vehicle, is between -7 and 107.


What do i do with the margins of error1
What do I do with the Margins of Error?

  • Take a look at them

  • Calculate the confidence interval

  • When margins of error are too big, combine estimates for small groups or small geographies – the Demographics & Workforce Group can help with this!

  • The most important step is #1. Always look at the margins of error of an estimate before using that estimate. If the margin of error is close to or bigger than the estimate, you should take further steps.

What else should i be aware of
What else should I be aware of?

  • Making comparisons

    • Do not compare multi-year estimates to single-year estimates

    • When comparing two areas, only use data from the same data series

    • If comparing, for example, Albemarle County and Greene County, use the data series they have in common – ACS 5-year estimates

What else should i be aware of1







What else should I be aware of?

  • Assessing Change

    • Do not assess year-to-year changes with multi-year estimates

    • Consecutive multi-year data contains data from overlapping years

    • The differences in overlapping estimates are driven by the differences in the non-overlapping years.

ACS 2005-2009 5-year Estimates

ACS 2006-2010 5-year Estimates

What else should i be aware of2
What else should I be aware of?

  • New American Factfinder

    • The Census Bureau is replacing their data access system with a new website

    • Right now, all ACS data are on the old system shown in the demo

  • Timeline

    • Late spring – Late summer 2011: ACS data will be phased into the new system

    • Fall 2011: Old Factfinder will be removed

  • Links


    • Tutorials:





American community survey 1353247

Susan Clapp